Transmission regulating system



Patented Apr. 26, 1938 UNITED STATES 2,115,141 TRANSMISSION REGULATIN G SYSTEM Curtis R. Eckberg,

Port Washington, N. Y., as-

signor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a. corporation of New York Application February 9, 1935, Serial No. 5,717

17 Claims.

This invention relates to wave transmission.

An object of the invention is to control such transmission, as for instance to control wave attenuation.

A further object is to control variation of transmission with frequency, as for instance variation of attenuation with frequency.

A further object is to compensate for change of attenuation of a circuit caused by change of conditions to which the circuit is subjected, as for example temperature or other weather conditions.

A further object is to compensate for variation of the attenuation change with frequency.

A further object is to vary the compensating attenuation smoothly.

A further object is to vary the compensating attenuation with one control.

Another object is to effect the compensation in response to the change of condition that causes the change of attenuation in the circuit.

It is also an object of the invention to obtain,

attenuation equal to any desired proportion of the total equalizer attenuation, the proportion being the same for all frequencies of the utilized frequency range.

For transmission circuits, for example cable carrier or open wire carrier telephone circuits, often attenuation equalizing systems are required giving variable attenuation equalization to compensate, over the transmission frequency range, for attenuation changes produced in the circuits by changes of temperature or other weather conditions to which the circuits are subjected. In one specific aspect the invention is such an attenuation equalizing system, with the required variable equalization obtained by adding to the output voltage of the usual equalizer network an adjustable voltage obtained from a potentiometer whose input is connected across the series arms of that network. The sum of the two voltages is applied to the grid circuit of a vacuum tube amplifier connected in the transmission circuit. The amount of equalization effected or amount of equalizing attenuation introduced is adjusted by varying the setting of the potentiometer. The adjustment may be made by means responsive to eiTects of the change of condition that produces the change of line attenuation. The potentiometer may be, for example, a resistance potentiometer or an air condenser potentiometer with relatively movable plates or armatures; and the latter type of potentiometer, affording smooth regulation and freedom from make-and-break contacts or sliding contacts in the transmission circuit, and requiring but little operating power, is of special utility when the regulation is effected automatically or in response to the change of conditions that produces theline attenuation change.

from an equalizer,

The imvacuum tube amplifier should does not materially change the pedance into the be high so that it impedances facing the line or equalizer network.

Other objects and aspects of the invention will be apparent from the following description and claims. V

Fig. 1 of the drawing is a circuit diagram of a system embodying one form of the invention; and r Fig. 1A shows a modification of that system.

In Fig. 1 an amplifier A, comprising vacuum tubes such as T, amplifies waves received over incoming line or circuit L and transmits the am plified waves to outgoing line or circuit L. The circuits L and L may be, for example, sections of a multiplex carrier cable or open wire circuit, the amplifier A amplifying simultaneously the waves of a number of carrier telephone channels and/or carrier telegraph channels, extending over a wide frequency range.

A transmission equalizing network E is provided for use in equalizing transmission variations over the carrier circuit, or compensating for variations in attenuation of the line, for example variations caused by change of temperature or other weather line is subjected. This network E has a suitable terminating impedance Z3, which may match the output impedance of the network. The network E may be an attenuation equalizer with its attenuation-frequency characteristic, (for transmission through the equalizer from its input terminals to its output terminals or terminating impedance), simulating the characteristic that represents the dilference between the line's highest and lowest attenuation-frequency characteristics for the range of temperature or'other variations for which attenuation equalization is desired, over the utilized frequency range. The

1,603,305, October 19, 1926 with one or more series arms conventionally shown as generalized impedances 3| and 32 and one or more, shunt arms conventionally shown as generalized impedance 33, 34 and 35. A potentiometer or voltage divider 10, comprising a resistance or impedance II and an adjustable contact 12 therefor, has its input leads l3 and 14 connected across the series arms of the equalizer E or so connected to the equalizer as to receive the difference between the conditions to which the 2 input and output voltages of the equalizer, i. e., the difference between the voltage across the line side of the equalizer and the voltage across the equalizer terminating resistance or impedance Z3. The output lead 15 cf the potentiometer I0 is connected to the grid of the first tube T of the amplifier A. Consequently, portion Y of the'potentiometer impedance H and the terminating impedance Z3 of equalizer E' are in serial relation to each other across the amplifier input. 7

V1, V2, and V3 designate the equalizer input voltage, the voltage the equalizer output voltage respectively.

expresses the equalizer attenuation,

V1 expresses the attenuation of that part of th potentiometer shown as X. Theselosses may also be considered as voltage differences and will then be expressed as V1V3 and V1-V2. Since V1V3 varies with frequency because the equalizer is designed to produce a loss variable with frequency, the voltage impressed upon the potentiometer is variable with frequency and the voltage measured between either end of the potention'ieter and the contactor I2 is variable with frequency. When the contactor is at the extreme left or input, V2=V1 and no part of the equalizer loss is introduced into the transmission circuit. The transmission circuit is the circuit through which waves are passed from origin to receiver and in this description includes only a part of the circuit shown on the drawing, that is, the input line, that part of the potentiometer shown as vX, amplifier A and the output line. As the contactor is moved towards the right it will be evident that the voltage between it and the left connection 13 is subtracted from the input voltage V1 .and since it is variable with frequency the resultant voltage V2 will be the input voltage minus some portion of the voltage difference between the input and output equalizer voltage.

. This is equivalent to adding into the transmission circuit an equalizer readily variable from zero to maximum loss in small steps. When the contactor is at the extreme right V2=V3 and all the equalizer loss is in the transmission circuit.

The action of the potentiometer may also be considered as adding to the output voltage of the equalizer, V3, the voltage between the contactor and the right connection 14. This is equivalent to removing from the transmission circuit an equalizer readily variable from maximum to zero loss in small steps.

The grid voltage V2 is expressed by the equation constant with frequencyand is called the flat loss, the other being variable with frequency,

and being called twist loss. If the'equalizer designincludes the total attenuation change, the

applied to the amplifier, and

method described herein will compensate for the total change. If the equalizer design includes only that part of the change variable with frequency the method will compensate only for the Variable component and it will be necessary to compensate for the flat loss by other means.

The adjustment of the contactor 12 may be made manually. However, if desired it may be 7 made automatically, for example through shaft I'l operated from pilot wire or pilot channel control equipment indicated at I6. For instance, the equipment l6 may be automatic pilot wire transmission regulator control equipment such as that which operates transmission regulating rheostat 12 of the system disclosed in H. S. Black Patent 1,956,547, May 1, 1934, ton-Edwards Patent 1,960,350, May 29, 1934; or maybe automatic pilot channel transmission regulator control equipment such as that which operates the equalizer-potentiometer 36, 3! of Afiel Patent 1,511,013, October, '7, 1924 or such as that of .R. W. Chesnut Patent 2,049,195, July 28, 1936.

Fig. 1A shows a modification of the portion of Fig. 1 above line B-B, in that there is substituted for the resistance potentiometer II] a condenser potentiometer I6 comprising fixed condenser plates or' armatures l8 and I9 and relatively movable plate or armature 20 cooperating therewith. The impedance of the condenser potentiometer across the equalizer is not independent of frequency but the action of the condenser poj to that of the resisttentiometer is comparable ance potentiometer for voltage dividing purposes, and in the case of automatic operation by equipment IS the condenser potentiometer has special utility because of its freedom from frictional power losses that would be entailed by employment or such as that of Shacklet of a potentiometer having moving electrical conriving from said network a voltage proportional to the diiference'between the input and output voltages of said equalizing network and. applying said derived voltage to said voltage divider. V 2. A wave translating system comprising a network including reactances and having attenuation varying with frequency over a given frequency range, a source of Voltage for supplying thereto'waves of said range, and attenuating means having substantially uniform attenuation over said range connected to said network for obtaining therefrom a voltage variable smoothly at each frequency of said range by the same proportion of the difference between the input and output voltages thereof.

3. A wave translating system comprising a transmission equalizing network having attenuation varying with frequency, a source of voltage for supplying waves thereto, a two-terminal impedance, and means connecting said network and said impedance for supplying across said two terminals a voltage proportional to the diiference between the input said network and giving to each point of said impedance between said two terminals instantan'eous potential variable with frequency and of 'magnitude within the range between the magnitudes of the terminal potentials.

4. The method of adjusting attenuation of a circuit including an attenuation equalizing netand output voltages of a for connecting work whose attenuation varies with frequency over a given frequency range, which comprises supplying to the network waves of the given frequency range, deriving from the network a voltage proportional to the difierence between its input and output voltages, attenuating said derived voltage substantially uniformly over the given frequency range, deriving from the output voltage of the network a voltage proportional to the network output voltage, and combining the latter derived voltage and said attenuated voltage, said combined voltage varying with frequency.

5. A wave translating system comprisingran equalizing network having attenuation varying with frequency over a given frequency range, a wave source for supplying input voltage thereto and creating output voltage thereof, adjustable attenuating means having substantially uniform attenuation over said frequency range associated with said network for deriving therefrom a variable voltage proportional to the difference between said input and output voltages, and a circuit for combining said derived voltage and said output voltage.

6. A wave translating system comprising a corrective network having a transmission characteristic varying with frequency, means for supplying waves thereto, a potentiometer having an input circuit and an output circuit, means for supplying to said input circuit a voltage proportional to the difference between the input and output voltages of the network, a voltage operated device having an input circuit, and means said output circuit of said potentiometer in said input circuit of said device.

7. A wave translating system comprising an equalizer network for correcting a transmission characteristic having input terminals and output terminals and having series and shunt impedance arms comprising reactances, with said series arms connected between one of said input terminals and one of said output terminals, a terminating impedance for said equalizer network connected across said output terminals, an outgoing circuit, and variable attenuating means comprising an impedance device connected across said series arms for supplying to saidcircuit the sum of the voltage across said terminating impedance and an adjustable portion of the voltage between said one input terminal and said one output terminal.

8. A wave translating system comprising an equalizer for correcting a transmission characteristic, a two-terminal impedance, means connecting said equalizer and said impedance for supplying across said two terminals a voltage proportional to the difference between the input and terminals is adjustable. V

9. A wave translating system comprising a network having attenuation varying with frequency, a terminating impedance for said net'- work, a two-terminal impedance, means connecting said network and said two-terminal impedance for supplying across said two terminals a voltage proportional to the difference between the input and output voltages of said network, and a circuit comprising said terminating impedance and connected to one of said terminals and having a connection to said two-terminal impedance dividing said two-terminal impedance output voltages of the equalizer, and a impedance values are wave transmission line subject to weather changes that vary its attenuation, a repeater and equalizer network therefor, and means comprising a gain control condenser potentiometer connetwork with the input of output voltage of said network. 7

14. The combination of a network including reactances and having attenuation variable with frequency-over a given frequency range, means for supplying thereto waves of said range, attenuating means having substantially uniform attenuation over said range connected to said network for obtaining therefrom a, voltage variable smoothly at each frequency of said range by the same proportion of the difference between operated device, and

resultant voltage to V stantially independent of frequencybut depend? cut on said adjustable attenuation.

lfipThe method of adjusting the transmission of a circuit including a transmission control network having reactive series and shunt arms giving the network a transmission characteristic variable with frequency, which comprises applying a voltage to the input of said network, deriving a voltage of given frequency from aselected portion of the series arms of the network, deriving a voltage of like frequency from a -selected portion of the shunt arms of the network, adjustably attenuating one of said derived voltages, and

combining said other derived voltage and said attenuated voltage to obtain an output voltage such that the transmission loss fro'm'said applied voltage to said output voltage is related to the network loss by a factor substantially independent of frequency but dependent on "said to any chosen portion of thedifference between the input and output voltages of the network, and a circuit for utilizing said derived voltage.

con'ris R. ECKBERG.

network in its output im- 

